Tell users about cabal.project.local~

.gitignore

@@ -50,6 +50,7 @@ ctags
 
 # stack artifacts
 /.stack-work/
+stack.yaml.lock
 
 # Shake artifacts
 .shake*
@@ -60,3 +61,6 @@ register.sh
 
 # python artifacts from documentation builds
 *.pyc
+
+# macOS folder metadata
+.DS_Store

cabal-install/Distribution/Client/CmdConfigure.hs

@@ -10,6 +10,7 @@ import Distribution.Client.Compat.Prelude
 import Prelude ()
 
 import System.Directory
+import System.FilePath
 import qualified Data.Map as Map
 
 import Distribution.Client.ProjectOrchestration
@@ -30,6 +31,9 @@ import Distribution.Simple.Command
 import Distribution.Simple.Utils
          ( wrapText, notice )
 
+import Distribution.Client.DistDirLayout
+         ( DistDirLayout(..) )
+
 configureCommand :: CommandUI (NixStyleFlags ())
 configureCommand = CommandUI {
   commandName         = "v2-configure",
@@ -93,10 +97,26 @@ configureAction flags@NixStyleFlags {..} _extraArgs globalFlags = do
     -- Write out the @cabal.project.local@ so it gets picked up by the
     -- planning phase. If old config exists, then print the contents
     -- before overwriting
-    exists <- doesFileExist "cabal.project.local"
+
+    let localFile = distProjectFile (distDirLayout baseCtx) "local"
+        -- | Chooses cabal.project.local~, or if it already exists
+        -- cabal.project.local~0, cabal.project.local~1 etc.
+        firstFreeBackup = firstFreeBackup' (0 :: Int)
+        firstFreeBackup' i = do
+          let backup = localFile <> "~" <> (if i <= 0 then "" else show (i - 1))
+          exists <- doesFileExist backup
+          if exists
+            then firstFreeBackup' (i + 1)
+            else return backup
+
+    -- If cabal.project.local already exists, back up to cabal.project.local~[n]
+    exists <- doesFileExist localFile
     when exists $ do
-        notice verbosity "'cabal.project.local' file already exists. Now overwriting it."
-        copyFile "cabal.project.local" "cabal.project.local~"
+        backup <- firstFreeBackup
+        notice verbosity $
+          quote (takeFileName localFile) <> " already exists, backing it up to "
+          <> quote (takeFileName backup) <> "."
+        copyFile localFile backup
     writeProjectLocalExtraConfig (distDirLayout baseCtx)
                                  cliConfig
 
@@ -125,4 +145,5 @@ configureAction flags@NixStyleFlags {..} _extraArgs globalFlags = do
     verbosity = fromFlagOrDefault normal (configVerbosity configFlags)
     cliConfig = commandLineFlagsToProjectConfig globalFlags flags
                   mempty -- ClientInstallFlags, not needed here
+    quote s = "'" <> s <> "'"
 

cabal-install/Distribution/Client/TargetProblem.hs

@@ -45,8 +45,8 @@ data TargetProblem a
     | TargetProblemNoSuchPackage           PackageId
     | TargetProblemNoSuchComponent         PackageId ComponentName
 
-    | CustomTargetProblem a
       -- | A custom target problem
+    | CustomTargetProblem a
   deriving (Eq, Show, Functor)
 
 -- | Type alias for a 'TargetProblem' with no user-defined problems/errors.

cabal-testsuite/PackageTests/NewConfigure/LocalConfigOverwrite/cabal.out

@@ -1,6 +1,31 @@
 # cabal v2-configure
-'cabal.project.local' file already exists. Now overwriting it.
+'cabal.project.local' already exists, backing it up to 'cabal.project.local~'.
 Resolving dependencies...
 Build profile: -w ghc-<GHCVER> -O1
 In order, the following would be built:
  - NewConfigure-0.1.0.0 (lib) (first run)
+# cabal v2-configure
+'cabal.project.local' already exists, backing it up to 'cabal.project.local~0'.
+Build profile: -w ghc-<GHCVER> -O1
+In order, the following would be built:
+ - NewConfigure-0.1.0.0 (lib) (first run)
+# cabal v2-configure
+'cabal.project.local' already exists, backing it up to 'cabal.project.local~1'.
+Build profile: -w ghc-<GHCVER> -O1
+In order, the following would be built:
+ - NewConfigure-0.1.0.0 (lib) (first run)
+# cabal v2-configure
+'foo.project.local' already exists, backing it up to 'foo.project.local~'.
+Build profile: -w ghc-<GHCVER> -O1
+In order, the following would be built:
+ - NewConfigure-0.1.0.0 (lib) (first run)
+# cabal v2-configure
+'foo.project.local' already exists, backing it up to 'foo.project.local~0'.
+Build profile: -w ghc-<GHCVER> -O1
+In order, the following would be built:
+ - NewConfigure-0.1.0.0 (lib) (first run)
+# cabal v2-configure
+'foo.project.local' already exists, backing it up to 'foo.project.local~1'.
+Build profile: -w ghc-<GHCVER> -O1
+In order, the following would be built:
+ - NewConfigure-0.1.0.0 (lib) (first run)

cabal-testsuite/PackageTests/NewConfigure/LocalConfigOverwrite/cabal.test.hs

@@ -2,5 +2,20 @@ import Test.Cabal.Prelude
 
 main = cabalTest $
     withSourceCopy $ do
-        r <- cabal' "v2-configure" []
-        assertOutputContains "Now overwriting it" r
+        cabal' "v2-configure" [] >>=
+            assertOutputContains "backing it up to 'cabal.project.local~'"
+        cabal' "v2-configure" [] >>=
+            assertOutputContains "backing it up to 'cabal.project.local~0'"
+        cabal' "v2-configure" [] >>=
+            assertOutputContains "backing it up to 'cabal.project.local~1'"
+
+        -- With --project-file
+        cabal' "v2-configure" ["--project-file", "foo.project"] >>=
+            assertOutputContains
+                "'foo.project.local' already exists, backing it up to 'foo.project.local~'"
+        cabal' "v2-configure" ["--project-file", "foo.project"] >>=
+            assertOutputContains
+                "'foo.project.local' already exists, backing it up to 'foo.project.local~0'"
+        cabal' "v2-configure" ["--project-file", "foo.project"] >>=
+            assertOutputContains
+                "'foo.project.local' already exists, backing it up to 'foo.project.local~1'"

cabal-testsuite/PackageTests/NewConfigure/LocalConfigOverwrite/foo.project

@@ -0,0 +1 @@
+packages: .